Method and apparatus for determining transmission power of preamble in wireless communication system

ABSTRACT

Provided are a method and an apparatus for determining transmission power of a preamble in a wireless communication system. A terminal estimates secondary cell (SCell) path loss with respect to a downlink (DL) component carrier (CC), which is in a linkage relationship with an uplink (UL) component carrier inside the SCell; decides the transmission power of a physical random access channel (PRACH) preamble based on the SCell path loss that is estimated; and transmits the PRACH preamble to a base station through the UL CC inside the SCell, based on the transmission power that is decided, wherein the SCell and a primary cell (PCell) comprises a carrier aggregation (CA) system, the PCell is a cell from which the terminal performs radio resource control (RRC) connection with the base station, and wherein the Scell is at least one cell from residual cells in the carrier aggregation excluding the PCell.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for determining transmissionpower of a preamble in a wireless communication system.

2. Related Art

The next-generation multimedia wireless communication systems which arerecently being actively researched are required to process and transmitvarious pieces of information, such as video and wireless data as wellas the initial voice-centered services. The 4^(th) generation wirelesscommunication systems which are now being developed subsequently to the3^(rd) generation wireless communication systems are aiming atsupporting high-speed data service of downlink 1 Gbps (Gigabits persecond) and uplink 500 Mbps (Megabits per second). The object of thewireless communication system is to establish reliable communicationsbetween a number of users irrespective of their positions and mobility.However, a wireless channel has abnormal characteristics, such as pathloss, noise, a fading phenomenon due to multi-path, inter-symbolinterference (ISI), and the Doppler Effect resulting from the mobilityof a user equipment. A variety of techniques are being developed inorder to overcome the abnormal characteristics of the wireless channeland to increase the reliability of wireless communication.

A carrier aggregation (CA) which supports a plurality of cells may beapplied in a 3GPP LTE-A. The CA may be referred to as another name suchas a bandwidth aggregation. The CA refers to forming a broadband bycollecting one or more carrier having a bandwidth smaller than thebroadband when a wireless communication system tries to support thebroadband. The carrier which becomes a subject when collecting one ormore carrier may use the bandwidth which is used in the existing systemfor backward compatibility. For example, in 3GPP LTE, the bandwidths of1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz are supported, and in3GPP LTE-A, the broadband of more than 20 MHz may be formed by usingonly the bandwidth of the 3GPP LTE system. Furthermore, the broadbandmay be formed by defining a new bandwidth without using the bandwidth ofthe conventional system as itself.

A random access procedure is a procedure which is performed for a userequipment (UE) to connect to a base station. The UE may perform therandom access procedure by transmitting a random access preamble to thebase station. When the CA is supported, the UE may perform the randomaccess procedure for a plurality of cells.

When the CA is supported, there is a need for a method for efficientlydetermining transmission power of the random access preamble in therandom access procedure for the plurality of cells.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for determiningtransmission power of a preamble in a wireless communication system. Thepresent invention provides a method for determining transmission powerof a physical random access channel (PRACH) preamble in a random accessprocedure for a secondary cell (SCell) of a user equipment (UE)initialized by an order of a base station. The present inventionprovides a method of determining transmission power of the PRACHpreamble based on a downlink (DL) path loss of the SCell.

In an aspect, a method of determining, by a user equipment (UE),transmission power of a preamble in a wireless communication system isprovided. The method includes estimating a secondary cell (Scell) pathloss for a downlink (DL) component carrier (CC) which has a linkage withan uplink (UL) component carrier (CC) in a SCell, determiningtransmission power of a physical random access channel (PRACH) preamblebased on the estimated SCell path loss, and transmitting the PRACHpreamble to a base station through the UL CC in the SCell based on thedetermined transmission power. The SCell and a primary cell (PCell)consist of a carrier aggregation (CA), the PCell is a cell where the UEperforms radio resource control (RRC) connection with the base station,and the SCell is at least one cell among the remaining cells excludingthe PCell in the carrier aggregation.

The DL CC may have a SystemInformationBlockType2 (SIB2) linkage with theUL CC in the SCell.

The transmission power of the PRACH preamble may be determined by anequation

P _(PRACH)=min{P _(CAMX,c)(i), REAMBLE_RECEIVED_TARGET_POWER+PLc}[dBm],

wherein P_(CAMX,c)(i) is a transmission power of the UE defined forsubframe i of the PCell, and the PLc is the estimated SCell path loss.

The transmission power of the PRACH preamble may be determined based ona difference between a PCell path loss and the estimated SCell pathloss.

The transmission power of the PRACH preamble may be determined by anequation

P _(PRACH)=min{P _(CAMX,c)(i)PREAMBLE_RECEIVED_TARGET_POWER+PLc+PL_(diff)}[dBm],

wherein P_(CAMX,c)(i) is a transmission power of the UE defined forsubframe i of the PCell, the PLc is the estimated SCell path loss, andPL_(diff) is the difference between the PCell path loss and theestimated SCell path loss.

The difference between the PCell path loss and the estimated SCell pathloss may be received from the base station.

The difference between the PCell path loss and the estimated SCell pathloss may be received from the base station through one of a radioresource control (RRC) layer, a media access control (MAC) layer, and aphysical (PHY) layer.

The difference between the PCell path loss and the estimated SCell pathloss may be received from the base station through a physical downlinkcontrol channel (PDCCH) order.

The difference between the PCell path loss and the estimated SCell pathloss may be included in a downlink control information (DCI) format 1Aand is received from the base station through the PDCCH order.

The UL CC in the SCell may be a UL extension carrier which cannotoperate as a stand-alone carrier.

The DL CC may have a virtual linkage with the UL extension carrier.

The DL CC which has a virtual linkage with the UL extension carrier maybe indicated by the base station through a higher layer.

The DL CC which has a virtual linkage with the UL extension carrier maybe predetermined.

The PCell may provide at least one of non-access stratum (NAS) mobilityinformation and a security input at the time of RRC establishment, RRCreestablishment or a handover.

In another aspect, a user equipment (UE) for determining transmissionpower of a preamble in a wireless communication system is provided. TheUE includes a radio frequency (RF) unit for transmitting or receiving aradio signal, and a processor which is connected to the RF unit, andconfigured to estimate a secondary cell (Scell) path loss for a downlink(DL) component carrier (CC) which has a linkage with an uplink (UL)component carrier (CC) in a SCell, determine transmission power of aphysical random access channel (PRACH) preamble based on the estimatedSCell path loss, and transmit the PRACH preamble to a base stationthrough the UL CC in the SCell based on the determined transmissionpower. The SCell and a primary cell (PCell) consist of a carrieraggregation (CA), the PCell is a cell where the UE performs radioresource control (RRC) connection with the base station, and the SCellis at least one cell among the remaining cells excluding the PCell inthe carrier aggregation.

When a random access procedure for a SCell of a UE is initialized by anorder of a base station, transmission power of a PRACH preamble may beeffectively determined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

FIG. 3 shows an example of a resource grid of a single downlink slot.

FIG. 4 shows the structure of a downlink subframe.

FIG. 5 shows the structure of an uplink subframe.

FIG. 6 shows an example of a subframe structure of 3GPP LTE-A systemwhich is cross-carrier-scheduled through CIF.

FIG. 7 shows an example where two cells have different UL transmissiontimings in a CA environment.

FIG. 8 shows an example of initializing a random access process for aSCell of a UE by an order of a base station.

FIG. 9 shows an example of a general random access process.

FIG. 10 shows an embodiment of a proposed method of determiningtransmission power of a preamble.

FIG. 11 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following technique may be used for various wireless communicationsystems such as code division multiple access (CDMA), a frequencydivision multiple access (FDMA), time division multiple access (TDMA),orthogonal frequency division multiple access (OFDMA), singlecarrier-frequency division multiple access (SC-FDMA), and the like. TheCDMA may be implemented as a radio technology such as universalterrestrial radio access (UTRA) or CDMA2000. The TDMA may be implementedas a radio technology such as a global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, E-UTRA (Evolved UTRA), andthe like. IEEE 802.16m, an evolution of IEEE 802.16e, provides backwardcompatibility with a system based on IEEE 802.16e. The UTRA is part of auniversal mobile telecommunications system (UMTS). 3^(rd) generationpartnership project (3GPP) long term evolution (LTE) is part of anevolved UMTS (E-UMTS) using the E-UTRA, which employs the OFDMA indownlink and the SC-FDMA in uplink. LTE-advanced (LTE-A) is an evolutionof 3GPP LTE.

Hereinafter, for clarification, LTE-A will be largely described, but thetechnical concept of the present invention is not meant to be limitedthereto.

FIG. 1 shows a wireless communication system.

The wireless communication system 10 includes at least one base station(BS) 11. Respective BSs 11 provide a communication service to particulargeographical areas 15 a, 15 b, and 15 c (which are generally calledcells). Each cell may be divided into a plurality of areas (which arecalled sectors). A user equipment (UE) 12 may be fixed or mobile and maybe referred to by other names such as mobile station (MS), mobileterminal (MT), user terminal (UT), subscriber station (SS), wirelessdevice, personal digital assistant (PDA), wireless modem, handhelddevice. The BS 11 generally refers to a fixed station that communicateswith the UE 12 and may be called by other names such as evolved-NodeB(eNB), base transceiver system (BTS), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongsis called a serving cell. A BS providing a communication service to theserving cell is called a serving BS. The wireless communication systemis a cellular system, so a different cell adjacent to the serving cellexists. The different cell adjacent to the serving cell is called aneighbor cell. A BS providing a communication service to the neighborcell is called a neighbor BS. The serving cell and the neighbor cell arerelatively determined based on a UE.

This technique can be used for downlink or uplink. In general, downlinkrefers to communication from the BS 11 to the UE 12, and uplink refersto communication from the UE 12 to the BS 11. In downlink, a transmittermay be part of the BS 11 and a receiver may be part of the UE 12. Inuplink, a transmitter may be part of the UE 12 and a receiver may bepart of the BS 11.

The wireless communication system may be any one of a multiple-inputmultiple-output (MIMO) system, a multiple-input single-output (MISO)system, a single-input single-output (SISO) system, and a single-inputmultiple-output (SIMO) system. The MIMO system uses a plurality oftransmission antennas and a plurality of reception antennas. The MISOsystem uses a plurality of transmission antennas and a single receptionantenna. The SISO system uses a single transmission antenna and a singlereception antenna. The SIMO system uses a single transmission antennaand a plurality of reception antennas. Hereinafter, a transmissionantenna refers to a physical or logical antenna used for transmitting asignal or a stream, and a reception antenna refers to a physical orlogical antenna used for receiving a signal or a stream.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

It may be referred to Paragraph 5 of “Technical Specification GroupRadio Access Network; Evolved Universal Terrestrial Radio Access(E-UTRA); Physical channels and modulation (Release 8)” to 3GPP (3rdgeneration partnership project) TS 36.211 V8.2.0 (2008-03). Referring toFIG. 2, the radio frame includes 10 subframes, and one subframe includestwo slots. The slots in the radio frame are numbered by #0 to #19. Atime taken for transmitting one subframe is called a transmission timeinterval (TTI). The TTI may be a scheduling unit for a datatransmission. For example, a radio frame may have a length of 10 ms, asubframe may have a length of 1 ms, and a slot may have a length of 0.5ms.

One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in a time domain and a plurality ofsubcarriers in a frequency domain. Since 3GPP LTE uses OFDMA indownlink, the OFDM symbols are used to express a symbol period. The OFDMsymbols may be called by other names depending on a multiple-accessscheme. For example, when SC-FDMA is in use as an uplink multi-accessscheme, the OFDM symbols may be called SC-FDMA symbols. A resource block(RB), a resource allocation unit, includes a plurality of continuoussubcarriers in a slot. The structure of the radio frame is merely anexample. Namely, the number of subframes included in a radio frame, thenumber of slots included in a subframe, or the number of OFDM symbolsincluded in a slot may vary.

3GPP LTE defines that one slot includes seven OFDM symbols in a normalcyclic prefix (CP) and one slot includes six OFDM symbols in an extendedCP.

The wireless communication system may be divided into a frequencydivision duplex (FDD) scheme and a time division duplex (TDD) scheme.According to the FDD scheme, an uplink transmission and a downlinktransmission are made at different frequency bands. According to the TDDscheme, an uplink transmission and a downlink transmission are madeduring different periods of time at the same frequency band. A channelresponse of the TDD scheme is substantially reciprocal. This means thata downlink channel response and an uplink channel response are almostthe same in a given frequency band. Thus, the TDD-based wirelesscommunication system is advantageous in that the downlink channelresponse can be obtained from the uplink channel response. In the TDDscheme, the entire frequency band is time-divided for uplink anddownlink transmissions, so a downlink transmission by the BS and anuplink transmission by the UE can be simultaneously performed. In a TDDsystem in which an uplink transmission and a downlink transmission arediscriminated in units of subframes, the uplink transmission and thedownlink transmission are performed in different subframes.

FIG. 3 shows an example of a resource grid of a single downlink slot.

A downlink slot includes a plurality of OFDM symbols in the time domainand N_(RB) number of resource blocks (RBs) in the frequency domain. TheN_(RB) number of resource blocks included in the downlink slot isdependent upon a downlink transmission bandwidth set in a cell. Forexample, in an LTE system, N_(RB) may be any one of 60 to 110. Oneresource block includes a plurality of subcarriers in the frequencydomain. An uplink slot may have the same structure as that of thedownlink slot.

Each element on the resource grid is called a resource element. Theresource elements on the resource grid can be discriminated by a pair ofindexes (k,l) in the slot. Here, k (k=0, . . . , N_(RB)×12-1) is asubcarrier index in the frequency domain, and 1 is an OFDM symbol indexin the time domain.

Here, it is illustrated that one resource block includes 7×12 resourceelements made up of seven OFDM symbols in the time domain and twelvesubcarriers in the frequency domain, but the number of OFDM symbols andthe number of subcarriers in the resource block are not limited thereto.The number of OFDM symbols and the number of subcarriers may varydepending on the length of a cyclic prefix (CP), frequency spacing, andthe like. For example, in case of a normal CP, the number of OFDMsymbols is 7, and in case of an extended CP, the number of OFDM symbolsis 6. One of 128, 256, 512, 1024, 1536, and 2048 may be selectively usedas the number of subcarriers in one OFDM symbol.

FIG. 4 shows the structure of a downlink subframe.

A downlink subframe includes two slots in the time domain, and each ofthe slots includes seven OFDM symbols in the normal CP. First three OFDMsymbols (maximum four OFDM symbols with respect to a 1.4 MHz bandwidth)of a first slot in the subframe corresponds to a control region to whichcontrol channels are allocated, and the other remaining OFDM symbolscorrespond to a data region to which a physical downlink shared channel(PDSCH) is allocated.

The PDCCH may carry a transmission format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a PCH, systeminformation on a DL-SCH, a resource allocation of an higher layercontrol message such as a random access response transmitted via aPDSCH, a set of transmission power control commands with respect toindividual UEs in a certain UE group, an activation of a voice overinternet protocol (VoIP), and the like. A plurality of PDCCHs may betransmitted in the control region, and a UE can monitor a plurality ofPDCCHs. The PDCCHs are transmitted on one or an aggregation of aplurality of consecutive control channel elements (CCE). The CCE is alogical allocation unit used to provide a coding rate according to thestate of a wireless channel. The CCD corresponds to a plurality ofresource element groups. The format of the PDCCH and an available numberof bits of the PDCCH are determined according to an associative relationbetween the number of the CCEs and a coding rate provided by the CCEs.

The BS determines a PDCCH format according to a DCI to be transmitted tothe UE, and attaches a cyclic redundancy check (CRC) to the DCI. Aunique radio network temporary identifier (RNTI) is masked on the CRCaccording to the owner or the purpose of the PDCCH. In case of a PDCCHfor a particular UE, a unique identifier, e.g., a cell-RNTI (C-RNTI), ofthe UE, may be masked on the CRC. Or, in case of a PDCCH for a pagingmessage, a paging indication identifier, e.g., a paging-RNTI (P-RNTI),may be masked on the CRC. In case of a PDCCH for a system informationblock (SIB), a system information identifier, e.g., a systeminformation-RNTI (SI-RNTI), may be masked on the CRC. In order toindicate a random access response, i.e., a response to a transmission ofa random access preamble of the UE, a random access-RNTI (RA-RNTI) maybe masked on the CRC.

FIG. 5 shows the structure of an uplink subframe.

An uplink subframe may be divided into a control region and a dataregion in the frequency domain. A physical uplink control channel(PUCCH) for transmitting uplink control information is allocated to thecontrol region. A physical uplink shared channel (PUCCH) fortransmitting data is allocated to the data region. When indicated by ahigher layer, the UE may support a simultaneous transmission of thePUSCH and the PUCCH.

The PUCCH with respect to a UE is allocated by a pair of resource blocksin a subframe. The resource blocks belonging to the pair of resourceblocks (RBs) occupy different subcarriers in first and second slots,respectively. The frequency occupied by the RBs belonging to the pair ofRBs is changed based on a slot boundary. This is said that the pair ofRBs allocated to the PUCCH is frequency-hopped at the slot boundary. TheUE can obtain a frequency diversity gain by transmitting uplink controlinformation through different subcarriers according to time. In FIG. 5,m is a position index indicating the logical frequency domain positionsof the pair of RBs allocated to the PUCCH in the subframe.

Uplink control information transmitted on the PUCCH may include a hybridautomatic repeat request (HARQ) acknowledgement/non-acknowledgement(ACK/NACK), a channel quality indicator (CQI) indicating the state of adownlink channel, a scheduling request (SR), and the like.

The PUSCH is mapped to an uplink shared channel (UL-SCH), a transportchannel. Uplink data transmitted on the PUSCH may be a transport block,a data block for the UL-SCH transmitted during the TTI. The transportblock may be user information. Or, the uplink data may be multiplexeddata. The multiplexed data may be data obtained by multiplexing thetransport block for the UL-SCH and control information. For example,control information multiplexed to data may include a CQI, a precodingmatrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Orthe uplink data may include only control information.

In 3GPP LTE-A, a carrier aggregation (CA) which supports a plurality ofcells may be applied. A plurality of base stations and UEs maycommunicate through up to 5 cells. The 5 cells may correspond to thebandwidth of the maximum 100 MHz. That is, the CA environment indicatesa case where a specific UE has two or more configured serving cells(hereinafter, referred to as “cell”) having different carrierfrequencies. The carrier frequency represents the center frequency of acell.

A cell shows combination of DL resources and optionally UL resources.That is, the cell certainly includes DL resources, and the UL resourcescombined with the DL resources may be optionally included. The DLresources may be a DL component carrier (CC). The UL resources may be aUL CC. When a specific UE includes one configured serving cell, the UEmay include one DL CC and one UL CC. When a specific UE includes two ormore cells, the UE may include DL CCs whose number is the same as thenumber of cells and UL CCs whose number is the same as or smaller thanthe number of cells. That is, when CA is supported in the current 3GPPLTE-A, the number of DL CCs may always be the same as or greater thanthe number of UL CCs. However, in the release after 3GPP LTE-A, a CAwhere the number of DL CCs is smaller than the number of UL CCs may besupported.

The linkage between the carrier frequency of the DL CC and the carrierfrequency of the UL CC may be indicated by system informationtransmitted on the DL CC. The system information may be a systeminformation block type 2 (SIB2).

The UE which supports the CA may use a primary cell (PCell) and one ormore secondary cells (SCell) for an increased bandwidth. That is, whenthere are two or more cells, one cell becomes a PCell, and the othercells become SCells. Both the PCell and the SCell may become a servingcell. The UE in the RRC_CONNECTED state where the CA is not supported orcannot be supported may have only one serving cell including only thePCell. The UE in the RRC_CONNECTED state which supports the CA may haveone or more serving cells including the PCell and all SCells. Meanwhile,in the TDD system, the UL-DL configuration of all cells may be the same.

The PCell may be a cell which operates in a primary frequency. The PCellmay be a cell where the UE performs radio resource control (RRC)connection with a network. The PCell may be a cell whose cell index isthe smallest. The PCell may be a cell which tries a random accessthrough a physical random access channel (PRACH) firstly among aplurality of cells. The PCell may be a cell where the UE performs aninitial connection establishment process or a connectionre-establishment process in a CA environment. Furthermore, the PCell maybe a cell which is indicated in a handover process. The UE may obtainnon-access stratum (NAS) mobility information (e.g., a tracking areaindicator (TAI)) at the time of a RRCconnection/reestablishment/handover through the PCell. Furthermore, theUE may obtain a security input at the time of RRCreestablishment/handover through the PCell. The UE may be allocated andtransmit a PUCCH only in the PCell. Furthermore, the UE may apply systeminformation acquisition and system information change monitoring onlyfor the PCell. The network may change the PCell of the UE which supportsthe CA in the handover process by using RRCConnectionReconfigurationmessage including MobilityControlInfo.

The SCell may be a cell which operates in a secondary frequency. TheSCell is used to provide additional wireless resources. The PUCCH is notallocated to the SCell. When adding the SCell, the network provides allsystem information related with the operation of the related cell in theRRC_CONNECTED state to the UE through dedicated signaling. The change ofthe system information for the SCell may be performed by a release andaddition of the related cell, and the network may independently add,remove, or change the SCell through a RRC connection reestablishmentprocess which uses RRCConnectionReconfiguration message.

The LTE-A UE which supports the CA may simultaneously transmit orreceive one or a plurality of CCs depending on the capacity. The LTErel-8 UE may transmit or receive only one CC when each CC is compatiblewith the LTE rel-8 system. Hence, when the number of CCs used in the ULis the same as the number of CCs used in the DL, all CCs need to beconfigured to be compatible with the LTE rel-8. Furthermore, in order toefficiently use a plurality of CCs, a plurality of CCs may be managed ina media access control (MAC). When the CA is formed in the DL, thereceiver in the UE should be able to receive a plurality of DL CCs, andwhen the CA is formed in the UL, the transmitter in the UE should beable to transmit a plurality of UL CCs.

Furthermore, in the LTE-A system, a backward compatible carrier and anon-backward compatible carrier may exist. The backward compatiblecarrier is a carrier which can be connected to the UE of all LTEreleases including LTE rel-8 and LTE-A. The backward compatible carriermay operate as a single carrier or a CC that forms a CA. The backwardcompatible carrier may be formed always as a pair of DL and UL in a FDDsystem. In contrast, the non-backward compatible carrier cannot beconnected to the UE of the previous LTE release, and may be connectedonly to the UE of or after the LTE release that defines the carrier. Forexample, there may be a carrier which can be connected only to a UE ofLTE rel-11 and cannot be connected to the UEs of LTE rel-8 to LTErel-10. The non-backward compatible carrier may operate as a singlecarrier or as a CC which forms a CA as in the backward compatiblecarrier.

The extension carrier is a carrier which cannot operate as a singlecarrier. However, the extension carrier needs to be a CC which forms aCA including at least one carrier which can operate as a single carrier.Hereinafter, the non-backward compatible carrier is referred to as anextension carrier for the convenience of explanation. Generally, in LTErel-8/9/10, the DL CC and the UL CC in the cell have a SIB2 linkage. Forexample, if an UL grant is transmitted through a PDCCH which isallocated to the DL CC, the PUSCH is allocated to the UL CC which has aSIB2 linkage with the DL CC. Furthermore, the control channel in the DLand the UL may be performed based on the CC which has a SIB2 linkage.However, if the DL/UL extension carrier is defined, the DL/UL extensioncarrier does not have a UL/DL CC which has a SIB2 linkage.

As a CA environment is introduced, cross carrier scheduling may beapplied. Through the cross carrier scheduling, the PDCCH on a specificDL CC may schedule the PDSCH on one DL CC among a plurality of DL CCs orschedule the PUSCH on one UL CC among a plurality of UL CCs. A carrierindicator field (CIF) may be defined for the cross carrier scheduling.The CIF may be included in the DCI format which is transmitted on thePDCCH. Whether the CIF exists within the DCI format may be indicated bythe higher layer semi-statically or UE-specifically. When the crosscarrier scheduling is performed, the CIF may indicate the DL CC wherethe PDSCH is scheduled or the UL CC where the PUSCH is scheduled. TheCIF may be fixed three bits, and may exist in a fixed positionregardless of the DCI format size. When the CIF does not exist withinthe DCI format, the PDCCH on a specific DL CC may schedule the PDSCH onthe same DL CC or schedule the PUSCH on the UL CC which has a SIB2linkage with the specific DL CC.

When the cross carrier scheduling is performed using the CIF, the basestation may allocate the PDCCH monitoring DL CC aggregation in order toreduce complexity of the blind decoding of the UE. The PDCCH monitoringDL CC aggregation is a part of the whole DL CC, and the UE performsblind decoding only for the PDCCH within the PDCCH monitoring DL CCaggregation. That is, in order to schedule the PDSCH and/or PUSCH forthe UE, the base station may transmit the PDCCH only through the DL CCin the PDCCH monitoring DL CC aggregation. The PDCCH monitoring DL CCaggregation may be set UE-specifically, UE-group-specifically orcell-specifically.

FIG. 6 shows an example of a subframe structure of 3GPP LTE-A systemwhich is cross-carrier-scheduled through CIF.

Referring to FIG. 6, a first DL CC among three DL CCs is set as a PDCCHmonitoring DL CC. When the cross carrier scheduling is not performed,each DL CC schedules PDSCH by transmitting each PDCCH. When the crosscarrier scheduling is performed, only the first DL CC which is set asthe PDCCH monitoring DL CC transmits the PDCCH. The PDCCH which istransmitted on the first DL CC schedules the PDSCH of the second DL CCand the third DL CC by using CIF as well as the PDSCH of the first DLCC. The second DL CC and the third DL CC which are not set as the PDCCHmonitoring DL CC do not transmit PDCCH.

Furthermore, the cross carrier scheduling is not supported in the PCell.That is, the PCell is always scheduled by its own PDCCH. The UL grantand DL assignment of the cell is always scheduled from the same cell.That is, if the DL in the cell is scheduled on the second carrier, theUL is also scheduled on the second carrier. The PDCCH order may betransmitted only on the PCell. Furthermore, frame timing, a super framenumber (SFN) timing, etc. may be aligned in the aggregated cells.

Furthermore, the UE may transmit uplink control information such as anACK/NACK signal and channel state information (CSI) which are received,detected, or measured from one or more DL CCs, to the base stationthrough one predetermined UL CC. For example, when the UE needs totransmit an ACK/NACK signal for data which is received from DL CCs ofPCell and SCells, the UE may transmit a plurality of ACK/NACK signalsfor the data received from each DL CC to the base station through thePUCCH of the UL CC of the PCell by multiplexing or bundling the ACK/NACKsignals.

When supporting the CA, the intra-band CA and the inter-band CA may beconsidered. Generally, the intra-band CA is first considered. At thistime, the band refers to an operating bandwidth, and is defined as afrequency range where the system operates. Table 1 represents an exampleof an operating bandwidth which is used in 3GPP LTE. Table 5.5-1 of 3GPPTS 36.104 V10.0.0 may be referenced.

TABLE 1 E- UTRA Oper- ating UL Du- band- operating bandwidth DLoperating bandwidth plex width F_(UL) _(—) _(low)-F_(UL) _(—) _(high)F_(DL) _(—) _(low)-F_(DL) _(—) _(high) mode 1 1920 MHz-1980 MHz 2110MHz-2170 MHz FDD 2 1850 MHz-1910 MHz 1930 MHz-1990 MHz FDD 3 1710MHz-1785 MHz 1805 MHz-1880 MHz FDD 4 1710 MHz-1755 MHz 2110 MHz-2155 MHzFDD 5 824 MHz-849 MHz 869 MHz-894 MHz FDD 6 830 MHz-840 MHz 875 MHz-885MHz FDD 7 2500 MHz-2570 MHz 2620 MHz-2690 MHz FDD 8 880 MHz-915 MHz 925MHz-960 MHz FDD 9 1749.9 MHz-1784.9 MHz 1844.9 MHz-1879.9 MHz FDD 101710 MHz-1770 MHz 2110 MHz-2170 MHz FDD 11 1427.9 MHz-1447.9 MHz 1475.9MHz-1495.9 MHz FDD 12 698 MHz-716 MHz 728 MHz-746 MHz FDD 13 777 MHz-787MHz 746 MHz-756 MHz FDD 14 788 MHz-798 MHz 758 MHz-768 MHz FDD 15Reserved Reserved FDD 16 Reserved Reserved FDD 17 704 MHz-716 MHz 734MHz-746 MHz FDD 18 815 MHz-830 MHz 860 MHz-875 MHz FDD 19 830 MHz-845MHz 875 MHz-890 MHz FDD 20 832 MHz-862 MHz 791 MHz-821 MHz 21 1447.9MHz-1462.9 MHz 1495.9 MHz-1510.9 MHz FDD . . . 33 1900 MHz-1920 MHz 1900MHz-1920 MHz TDD 34 2010 MHz-2025 MHz 2010 MHz-2025 MHz TDD 35 1850MHz-1910 MHz 1850 MHz-1910 MHz TDD 36 1930 MHz-1990 MHz 1930 MHz-1990MHz TDD 37 1910 MHz-1930 MHz 1910 MHz-1930 MHz TDD 38 2570 MHz-2620 MHz2570 MHz-2620 MHz TDD 39 1880 MHz-1920 MHz 1880 MHz-1920 MHz TDD 40 2300MHz-2400 MHz 2300 MHz-2400 MHz TDD 41 2496 MHz-2690 MHz 2496 MHz-2690MHz TDD

A plurality of DL CCs or UL CCs which form the CA environment in theintra-band CA are placed adjacent to the frequency domain. That is, theplurality of DL CCs or UL CCs which form the CA environment may bepositioned within the same operating bandwidth. Hence, each cell in theintra-band CA may be formed under a premise that respective cells havesimilar electric wave characteristics. At this time, the electric wavecharacteristics may include a propagation/path delay, a propagation/pathloss, and fading channel impact which may be changed according to thefrequency or central frequency. A plurality of CCs are positioned withinthe same operating bandwidth, and thus the UE may obtain the ULtransmission timing for the UL CC in the PCell and set the ULtransmission timing of the UL CCs in the SCells to be the same as thetransmission timing of the obtained PCell. As such, the UL subframeboundary between cells is aligned in the UE in the same manner, and theUE may communicate with the base station in the CA environment throughone radio frequency (RF). However, the PRACH transmission timing may bedifferent for each cell.

A plurality of DL CCs or UL CCs which form the CA environment in theinter-band CA may not be positioned adjacent to the frequency domain. Aplurality of CCs which form the CA environment may not be positionedadjacent to the frequency domain due to the allocation of remainingfrequencies and the reuse of the frequencies which have been used asanother usage, etc. For example, when 2 cells form a CA environment, thecarrier frequency of one cell is 800 MHz in DL and UL, and the carrierfrequency of the other cell may be 2.5 GHz in DL and UL. Furthermore,the carrier frequency of one cell may be 700 MHz in DL and UL, and thecarrier frequency of one cell may be 2.1 GHz in DL and 1.7 GHz in UL. Insuch an inter-band CA environment, it cannot be assumed that electricwave characteristics between respective cells are the same. That is, inthe inter-band CA environment, the UL subframe boundaries between cellscannot be aligned in the same manner, and different UL transmissiontimings may need to be obtained between cells. The UE may communicatewith the base station through a plurality of RFs in the inter-band CAenvironment.

FIG. 7 shows an example where two cells have different UL transmissiontimings in a CA environment.

FIG. 7-(a) shows the UL transmission timing of the first cell, and FIG.7-(b) shows the UL transmission timing of the second cell. Referring toFIG. 7, the base station transmits the DL signal at the same time pointthrough the first cell and the second cell. The UE receives the DLsignal through the first cell and the second cell. At this time, the DLpropagation delay of the second cell is greater than the DL propagationdelay of the first cell. That is, the DL signal through the second cellis more lately received than the DL signal through the first cell.Respective cells may have different timing advance (TA) values. In FIG.7, the TA value of the first cell is TA₁, and the TA value of the secondcell is TA₂. Respective cells may have different UL transmissiontimings. The UL subframe of the first cell and the UL subframe of thesecond cell are not aligned each other. Each cell needs to perform ULtransmission based on different TA values. The current 3GPP LTE-A doesnot support different UL transmission timings between cells.Furthermore, the UL propagation delay of the second cell is greater thanthe UL propagation delay of the first cell. It was assumed in FIG. 7that both DL and UL propagation delays of the second cell are greaterthan the DL and UL propagation delays of the first cell for theconvenience of description, but this is merely an example, and the DLpropagation delay may not be proportional to the UL propagation delay.

Hereinafter, a method of efficiently obtaining a plurality of ULtransmission timings when the CA is supported is described. The methodof obtaining a plurality of UL transmission timings described below maybe applied regardless of the UL access scheme. It is assumed below thatthe UL access scheme is SC-FDMA, but the method may also be applied tothe case when the UL access scheme is OFDMA.

1) When a specific SCell has been added by the base station, the randomaccess process for the SCell of the UE may be initialized. That is, if aspecific SCell is added, the UE may obtain the UL transmission timing ofthe SCell.

2) Alternatively, when a specific SCell is activated by the basestation, the random access process for the SCell of the UE may beinitialized. Even if the SCell is added, the SCell may not be activatedand may not be actually used. It is not efficient to obtain and maintainUL transmission timings of such SCell. Hence, the UE may obtain the ULtransmission timing of the SCell when a specific SCell is added andactivated.

3) Alternatively, the random access process for the SCell of the UE maybe initialized by the order of the base station. The base station mayorder the UE to perform the random access process for the SCell afterthe SCell is added or the SCell is activated. However, the time pointwhen the base station orders the UE to perform the random access processis not limited thereto. In the description below, for the convenience ofdescription, it is assumed that the base station orders the UE toperform the random access process after the SCell is activated. Forexample, the order of the base station may be the PDCCH order.

FIG. 8 shows an example of initializing a random access process for aSCell of a UE by an order of a base station.

Referring to FIG. 8, in step S50, the base station transmits an RRCreconfiguration message to the UE. The SCell may be added by the RRCreconfiguration message. In step S51, the UE transmits the RRCreconfiguration complete message to the base station as a response tothe RRC reconfiguration message. In step S52, the base station needsactivation of the added SCell. In step S53, the base station transmits aSCell activation message to the UE. In step S54, the UE transmits a HARQACK message for the SCell activation message. In step S55, the basestation initializes the random access process for the SCell. In stepS56, the base station transmits the PDCCH order to the UE. In step S57,the random access process for the SCell between the UE and the basestation is performed. In step S58, the UE adjusts the UL transmissiontiming and transmits data to the base station after completing therandom access process.

Meanwhile, in the above description, the SCell may be extended to theextension carrier. That is, in the above description, the SCell may bereplaced with an UL extension carrier. When a specific UL extensioncarrier is added, when the added specific UL extension carrier isactivated or by the order of the base station, the random access processfor the UL extension carrier of the UE may be initialized. When therandom access process for the UL extension carrier of the UE isinitialized by the order of the base station, the base station maynotify the UE to initialize the random access process in variousmethods. For example, the base station may notify the UE to initializethe random access process through a specific field within the RRCmessage used when adding the UL extension carrier or through a separateRRC message. Furthermore, the base station may notify the UE toinitialize the random access process through a specific field within theMAC message used when activating the added UL extension carrier or aseparate MAC message. Furthermore, whether to cross-carrier-schedule theUL extension carrier may be ordered by the higher layer, or the systemmay be configured so that the cross carrier scheduling may be alwaysperformed without an explicit order.

FIG. 9 shows an example of a general random access process.

The random access process may be divided into a content-based randomaccess process and a non-contention based random access process. Theabove-described random access process for the SCell may be performedthrough one or more predetermined methods among two random accessprocesses.

FIG. 9-(a) shows a contention-based random access process. In step S61,the UE transmits a random access preamble to the base station. Therandom access preamble may be referred to as a PRACH preamble.Furthermore, the random access preamble may be called a first message inthe random access process. In step S62, the base station transmits arandom access response to the UE as a response to the random accesspreamble. The random access preamble may be referred to as a RACHresponse. The random access response may be called a second message inthe random access process. In step S63, the UE performs the scheduledtransmission to the base station. The scheduled transmission may becalled a third message in the random access process. In step S64, thebase station transmits the contention resolution message to the UE. Thecontention resolution message may be called a fourth message in therandom access process.

FIG. 9-(b) shows a non-contention based random access process. In stepS70, the base station allocates a random access preamble to the UE. Instep S71, the UE transmits a first message to the base station. In stepS72, the base station transmits a second message to the UE as a responseto the first message.

In 3GPP LTE-A rel-10, the random access process is performed only in thePCell, and thus the transmission power of the PRACH preamble may bedetermined by estimating a path loss of the PCell. Equation 1 belowshows an example of an equation for determining transmission power ofthe PRACH preamble.

P _(PRACH)=min{P _(CAMX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PLc}[dBm]  [Equation 1]

In Equation 1, P_(CAMX,c)(i) denotes transmission power of theconfigured UE which is defined for subframe i of the PCell, and PL_(c)denotes the estimated DL path loss which is calculated for the PCell inthe UE.

As described above, in order to obtain a plurality of UL transmissiontimings, the random access process may be performed for the SCell. Whenthe random access process is performed for the SCell, a new method fordetermining the transmission power of the PRACH preamble transmitted inthe SCell is required. Hereinafter, a method of determining thetransmission power of the PRACH preamble proposed by the presentinvention is described. In the description below, the contention-basedrandom access process is illustrated, but the present invention is notlimited to the example, and the present invention may also be applied tothe non-contention-based random access process in the same manner.

1) The transmission power of the PRACH preamble may be determined byestimating the path loss of the SCell where the PRACH preamble istransmitted. That is, the path loss used to determine the transmissionpower of the PRACH preamble may be a path loss of the DL CC which has aSIB2 linkage with the UL CC in the SCell where the PRACH preamble istransmitted. Equation 2 shows an example of an equation which determinesthe transmission power of the PRACH preamble according to the proposedmethod of determining the PRACH preamble transmission power.

P _(PRACH)=min{P _(CAMX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PLc}[dBm]  [Equation 2]

Equation 2 may have the same form as that of Equation 1, and PL_(c) inEquation 2 denotes the estimated value of the DL path loss, which iscalculated in the UE, for the DL CC which has a SIB2 linkage with the ULCC in the SCell.

2) The transmission power of the PRACH preamble may be determined by thedifference between the path loss of the PCell and the path loss of theSCell where the PRACH preamble is transmitted. Equation 3 shows anotherexample of an equation of determining the transmission power of thePRACH preamble according to the proposed method of determining thetransmission power of the PRACH preamble.

P _(PRACH)=min{P _(CAMX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PLc+PL_(diff)}[dBm]  [Equation 3]

In Equation 3, P_(CAMX,c)(i) denotes transmission power of theconfigured UE which is defined for subframe i of the PCell, PL_(c)denotes the estimated DL path loss calculated in the UE for the PCell,and PL_(diff) denotes a difference between estimated DL path loss valuescalculated in the UE for the DL CC which has a SIB2 linkage with the ULCC in the PCell and the SCell. PL_(diff) is 0 when the PRACH preamble istransmitted in the PCell.

The base station may signal the difference between the path loss of thePCell and the path loss of the SCell, where the PRACH preamble istransmitted, to the UE, and the UE may determine the transmission powerof the PRACH preamble using the difference. The base station maytransmit the difference between the path loss of the PCell and the pathloss of the SCell to the UE through one of RRC signaling, MAC signal,and PHY signaling. Furthermore, the difference between the path loss ofthe PCell and the path loss of the SCell may be broadcast or unicast.The base station already serves UEs which support the CA, and thus theUL transmission power between the PCell and a specific SCell may beestimated. Equation 4 below shows another example of an equation whichdetermines the transmission power of the PRACH preamble according to theproposed method of determining the transmission power of the PRACHpreamble.

P _(PRACH)=min{P _(CAMX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PLc+PL_(diff)}[dBm]  [Equation 4]

In Equation 4, P_(CAMX,c)(i) denotes the transmission power of theconfigured UE which is defined for subframe i of the PCell, and PL_(c)denotes the estimated DL path loss calculated in the UE for the PCell,and PL_(diff) denotes a difference between estimated DL path loss valuescalculated in the UE for the DL CC which has a SIB2 linkage with the ULCC in the PCell and the SCell, which is signaled from the base station.PL_(diff) is 0 when the PRACH preamble is transmitted in the PCell.

Meanwhile, as described above, when the random access process for theSCell is initialized after the activation of the SCell by the order ofthe base station, the base station may notify the UE of theinitialization of the random access process through the PDCCH order.Hence, the base station may signal even the difference between the pathloss of the PCell and the path loss of the SCell through the PDCCHorder. At this time, the PDCCH order may be transmitted through thePCell and may also be transmitted through the SCell which performs therandom access process. The present invention is not limited thereto. Thebase station may notify the UE of the difference between the path lossof the PCell and the path loss of the SCell using a specific fieldwithin the DCI format which is transmitted through PDCCH. The basestation already serves UEs which support the CA, and thus the ULtransmission power difference between the PCell and a specific SCell maybe estimated.

The random access process which is initialized by the PDCCH order in the3GPP LTE-A is performed through DCI format 1A. The DCI format 1A mayrefer to Section 5.3.3.1.3 of 3GPP TS 36.212 V10.2.0 (2011-06). When theDCI format 1A is used for the random access process which is initializedby the PDCCH order, the specific fields indicates information for PRACH,and the remaining bits are filled with Os. For example, when the DCIformat 1A is used for the random access process which is initialized bythe PDCCH order, the DCI format 1A may include such fields as a CIF, aDCI format 0/1A differentiation flag, a localized/distributed virtual RB(VRB) assignment flag, a resource block assignment, a preamble index,and a PRACH mask index, and such fields as a HARQ process number and aDL assignment index may be filled with Os. At this time, the CIF may beincluded in the DIC format 1A only when the cross carrier scheduling isindicated by the higher layer and the DCI format 1A is transmitted in aUE-specific search space (USS). The CIF is not included in the DCIformat 1A when the cross carrier scheduling is not performed and the DCIformat 1A is transmitted through the common search space (CSS).

The base station may notify the UE of the difference between the pathloss of the PCell and the path loss of the SCell through the DCI format1A. When the DCI format 1A is used for a random access process which isinitialized by the PDCCH order, the remaining bits such as the HARQprocess number and the LD allocation index are generated. Likewise, thebase station may notify the UE of the difference between the path lossof the PCell and the path loss of the SCell through the remaining bits.

Equation 5 shows another example of an equation which determines thetransmission power of the PRACH preamble according to the proposedmethod of determining the transmission power of the PRACH preamble.

P _(PRACH)=min{P _(CAMX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PLc+PL_(diff)}[dBm]  [Equation 5]

In Equation 5, P_(CAMX,c)(i) denotes the transmission power of theconfigured UE which is defined for subframe i of the PCell, and PL_(c)denotes the estimated DL path loss calculated in the UE for the PCell.PL_(diff) denotes a difference between estimated DL path loss valuescalculated in the UE for the DL CC which has a SIB2 linkage with the ULCC in the PCell and the SCell, which is signaled from the base stationby the PDCCH order. PL_(diff) is 0 when the PRACH preamble istransmitted in the PCell. When the DCI format 1A is used for the randomaccess process which is initialized by the PDCCH order, the DCI format1A may include PL_(diff).

FIG. 10 shows an embodiment of a proposed method of determiningtransmission power of a preamble.

Referring to FIG. 10, in step S100, the UE estimates the DL path lossfor the DL CC in the SCell. In step S110, the UE determines thetransmission power of the PRACH preamble based on the DL path loss. Thetransmission power of the PRACH preamble may be determined by theabove-described Equations 2 to 5. In step S120, the UE transmits thePRACH preamble to the base station based on the determined transmissionpower.

It was assumed above that the SCell includes only one cell, but this isonly for the convenience of description, and the present invention isnot limited to this example That is, in the above description, the SCellmay be one cell group including one or more cells except the PCell.Likewise, the PCell may also be one cell group including the PCell andanother cell.

Furthermore, the method of determining the transmission power of thePRACH preamble is also possible when the UL extension carrier isdefined. The UL extension carrier does not have a DL CC which has a SIB2linkage, and thus in order to determine the transmission power of thePRACH preamble by equations 2 to 5, the DL CC, which is associated withthe UL extension carrier in another method, may need to be set.Furthermore, there is no DL CC which has a SIB linkage with the ULextension carrier, and thus always the cross carrier scheduling needs tobe performed. Hereinafter, when the UL extension carrier is defined, themethod of setting the DL CC associated with the UL extension carrier isdescribed.

1) The DL CC which is virtually linked with the UL extension carrier maybe indicated from the base station by the higher layer. The base stationmay indicate the DL CC which is virtually linked with the UL extensioncarrier through the RRC signaling or MAC signaling. For example, thephysical layer identity including the DL CC which is virtually linkedwith the UL extension carrier may be indicated through the “PhysCellID”which is the RRC parameter which indicates the physical layer identityof the cell. Furthermore, a new RRC parameter which indicates the DL CCwhich is virtually linked with the UL extension carrier may be defined.Furthermore, the DL CC which is virtually linked with the UL extensioncarrier may be indicated through the MAC message or RRC message whichactivates the UL extension carrier. Furthermore, the DL CC which isvirtually linked with the UL extension carrier may be indicated throughthe MAC message or RRC message which adds or change the UL extensioncarrier.

The cell group for supporting different UL transmission timings betweencells and/or supporting different TDD UL/DL configurations between cellsmay be defined. When the cell group is defined for the support ofdifferent UL transmission timings between cells, the cells which belongto one cell group may have the same UL transmission timing. Furthermore,when the cell group is defined for supporting different TDD UL/DLconfigurations between cells, the cells which belong to one cell groupmay include the same TDD UL/DL configuration. Even in such a case, avirtual linkage with the UL extension carrier may be defined.

2) The DL CC which is virtually linked with the UL extension carrier maybe always determined by a predetermined rule. For example, the ULextension carrier may be set to always have a virtual linkage with theDL CC in the PCell. Furthermore, the UL extension carrier may be set tobe virtually linked with the DL CC in the cell having the smallest indexamong cells. Furthermore, the UL extension carrier may be set to bevirtually linked with the DL CC in the cell having the smallest cellindex among the activated cells. Even when the cell group is defined,the DL CC having a definition of a virtual linkage with the UL extensioncarrier within the cell group may be predetermined.

FIG. 11 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

A BS 800 includes a processor 810, a memory 820, and a radio frequency(RF) unit 830. The processor 810 may be configured to implement proposedfunctions, procedures, and/or methods in this description. Layers of theradio interface protocol may be implemented in the processor 810. Thememory 820 is operatively coupled with the processor 810 and stores avariety of information to operate the processor 810. The RF unit 830 isoperatively coupled with the processor 810, and transmits and/orreceives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a RF unit 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 910. Thememory 920 is operatively coupled with the processor 910 and stores avariety of information to operate the processor 910. The RF unit 930 isoperatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

1-15. (canceled)
 16. A method for transmitting, by a user equipment(UE), a physical random access channel (PRACH) preamble in a wirelesscommunication system, the method comprising: determining a transmissionpower of the PRACH preamble by using a downlink (DL) pathloss of asecondary cell (SCell) according to equation below:P _(PRACH)=min{P _(CMAX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PL_(c)}_[dBm], where P_(PRACH) denotesthe transmission power of the PRACH preamble, P_(CMAX,c)(i) denotes aconfigured UE transmission power for subframe i of the SCell,PREAMBLE_RECEIVED_TARGET_POWER denotes a target preamble received power,and PL_(c) denotes the DL pathloss of the SCell; and transmitting thePRACH preamble to a network on the SCell according to the transmissionpower of the PRACH preamble.
 17. The method of claim 16, wherein theSCell belongs to a cell group not containing a primary cell (PCell). 18.The method of claim 17, wherein the cell group further includes one ormore SCells.
 19. The method of claim 17, wherein an uplink (UL)transmission timing is the same for all cells included in the cellgroup.
 20. The method of claim 16, further comprising calculating the DLpathloss of the SCell on a downlink component carrier (DL CC) of theSCell.
 21. The method of claim 16, wherein the PRACH preamble istransmitted on an uplink component carrier (UL CC) of the SCell.
 22. Themethod of claim 16, wherein linkage between a carrier frequency of a DLCC of the SCell and a carrier frequency of a UL CC of the SCell isindicated by system information.
 23. The method of claim 22, wherein thesystem information is a system information block (SIB) type
 2. 24. Themethod of claim 22, wherein the system information is received from thenetwork on a DL CC of the SCell.
 25. The method of claim 16, furthercomprising receiving a request for a random access procedure from thenetwork.
 26. A user equipment (UE) in a wireless communication system,the UE comprising: a memory; a radio frequency (RF) unit; and aprocessor, coupled to the memory and the RF unit, configured to:determine a transmission power of the PRACH preamble by using a downlink(DL) pathloss of a secondary cell (SCell) according to equation below:P _(PRACH)=min{P _(CMAX,c)(i),PREAMBLE_RECEIVED_TARGET_POWER+PL_(c)}_[dBm], where P_(PRACH) denotesthe transmission power of the PRACH preamble, P_(CMAX,c)(i) denotes aconfigured UE transmission power for subframe i of the SCell,PREAMBLE_RECEIVED_TARGET_POWER denotes a target preamble received power,and PL_(c) denotes the DL pathloss of the SCell, and control the RF unitto transmit the PRACH preamble to a network on the SCell according tothe transmission power of the PRACH preamble.
 27. The UE of claim 26,wherein the SCell belongs to a cell group not containing a primary cell(PCell).
 28. The UE of claim 27, wherein the cell group further includesone or more SCells.
 29. The UE of claim 27, wherein an uplink (UL)transmission timing is the same for all cells included in the cellgroup.
 30. The UE of claim 26, wherein the processor is furtherconfigured to calculate the DL pathloss of the SCell on a downlinkcomponent carrier (DL CC) of the SCell.
 31. The UE of claim 26, whereinthe PRACH preamble is transmitted on an uplink component carrier (UL CC)of the SCell.
 32. The UE of claim 26, wherein linkage between a carrierfrequency of a DL CC of the SCell and a carrier frequency of a UL CC ofthe SCell is indicated by system information.
 33. The UE of claim 32,wherein the system information is a system information block (SIB) type2.
 34. The UE of claim 32, wherein the system information is receivedfrom the network on a DL CC of the SCell.
 35. The UE of claim 26,wherein the processor is further configured to control the RF unit toreceive a request for a random access procedure from the network.